It is the purpose of the proposed research to determine the relative importance of early termination control and initiation control of arg mRNA synthesis in the regulation of expression of the argECBH cluster in E. coli. Experiments are designed to determine more exactly the origin and regulation of the formation of short versus long arg ECBH mRNA species. Studies are proposed to distinguish the suspected dual roles of the arginine argR protein complex in regulation of argECBH synthesis. In addition, the role of the arginyl-tRNA arg system and other cellular factors in regulation of early termination will be investigated. By determining the interrelationship between controls at initiation and possible early termination of arg-mRNA, it is hoped that the devices by which an organism regulates protein synthesis in response to changes in available nutrients will be better understood. Also because the argECBH cluster is a bipolar operon transcribing bidirectionally from an internal control region (EC boundary), these studies may reveal specific information about the strategy for control of transcription involving reading of both strands of DNA in the same region.